Surgical sawing instrument



April 3, 1951 J. (n. KARLE 2,547,707

SURGICAL SAWING INSTRUMENT Wi' ""llllllllll l" t n John g1g/@fifa prilf, :1951 J. p. KARL: 2,547,707

SURGICAL sAwING INSTRUMENT Fileduan. 15, 1947 3 Sheets-Sheet 2 SURGICAL SAWING INSTRUMENT Filed Jan. l5, 1947 3 SheetsSheet 3 Patented Apr. 3, 1951 2,547,707 SURGICL S'AWING INSTRUMENT John D. Karla-Roselle Park, N.

Singer Manufacturing Company,

J assigner to The Elizabeth,

N. J., a. corporation of New Jersey Application January 15, 1947, Serial No. '722,098 23 claims. (01428-317.)

This invention relates to surgical instruments and more particularly to an improved surgical saw which is specifically `adapted to partially cut out a section of skullbone, which sectionis thereafter brokenv along an uncut line, to form, in effect, a nap or trap door to give access to the brain. therebeneath, thereby to; permit the` performance of a brain operation.

The instrument disclosed in this. application is designed to be used .in conjunction with,A and as a complement to, the trephining instrument which forms thev subject of my pending United States patent application Serial No. 653,900, iiled Mar. 12, 1946, now Patent #2,504,075 as hereinafter is explained.

A primary object of this invention is to provide an improved skull saw which is of relatively vlight weight and which, therefore, may be handled with great facility; which will greatly reduce the time required for the opening of the skull; which will reduce, to a minimum, vibration reaction on the skull and brain and consequently the shock to the patient;v and which is adapted to cut in. a substantially smaller arc than any skull sawheretofore provided. Y

Another object of the invention is to provide an improved saw which will form an under cut in the bone so that thesection which is partially severed may readily be broken, tipped upwardly and backwardly to expose the dura andl the brain therebeneath, and finally be swung back intothe precise position which it initially occupied, for subsequent knitting to the adjacent surface of the skull bone.

A further object of thek invention is to provide, in an instrument of the type above described, improved means, under the control of the user, for conveniently starting and stopping the cutting action of the saw, at will, without releasing his normal grip on the instrument, whereby a more accurate control of the instrument is assured.

Another object of` the invention is to provide an improved construction in which the saw blade may be readily removed and replaced.

Still another object is to provide a readily removable saw guard and dura deilector which may be easily and conveniently removed for sterilization purposes.

With the above andv other objects in View, as will hereinafter appear, the invention comprises the devices, combinations and. arrangements of parts hereinafter set forth. and; illustrated. in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained. thereby will be skilled in'. the art..

In the drawings, Fig.. 1 is a side elevation. of a surgical instrument embodying the present invention, with partsof thev instrument illustrated, indotted lines,.in the positions which they occupy when the instrument is in use.

Fig. 2 is a longitudinal sectional view of the instrument, looking.'Y in the opposite direction.

Fig. 3 is a left end view of the instrument shown in Fig... 1.

Fig. 4 is a plan view of the instrument.

Fig. 5is a bottom: view thereof.

Fig. 6 is a front View of the head. of the instrument with the face plate thereof removed and with certain parts in section, showing more particularly the mounting of the saw bar and the saw blade and the means for reciprocating the saw bar.

Fig. 'l is an enlarged horizontal section taken substantially on the line 7-`l of Fig. 1.

Fig. 8 is a detail perspective view of a turnable saw guard, and dura deflector hereinafter to be described.

Fig. 9 is a perspective view of a shield member which is secured to the machine frame and which partially vsurrounds a portionv of theY hub of readily understood'by those Y the'sawl guard: and dura deilector.

Fig.. 10 is a detail sectional View taken through the saw blade andthe shank of the saw guardi and dura deecton, illustrating the angular arrangement of the saw blade relative to the sawV cut and the-manner in which the turnable'saw guard tracks the cut made in a skull bone bythe saw, thus permitting the saw to cut. in a relatively small arc..

Fig. l1 is a front end view of the instrument, illustrating it in the act of und-ercutting a skull section after the skull has been trephined by the instrument. disclosed in `my above mentioned patent application.

Fig. 12 is an enlarged sectional view taken substantially on they line l2-lf2 of Fig. 2, illustrating in full and dotted lines the two extreme positions of the shank of a guard and deilector member hereinafter to be described.

Fig. 13 is a diagrammatic illustration of the improved instrument, a remotely located driving motor connected to thel instrument by a flexible drive shaft, and an electrical circuit connecting the. instrument and motor for controlling the motor by a switch on the instrument.

Referring more specifically to the drawings, the' invention: is disclosed. as embodied in a surgical instrument comprising a frame I" having.

3 at .one end a hollow head 2 and, at its opposite end a portion 3 upon which is threaded one end of a hollow handle 4.

Journaled in a bearing bushing in the rear end of the handle 4 and in bearing bushings 6 and 1 in the frame I, is a rotatable shaft 8 having, at its rear end, a slot 3 into which is tted a flat driving tongue II] carried by a rotatable member II connected to and forming a part of a rotating core I2 of a conventional ilexible drive shaft S. The shaft S includes a non-rotatable armor I3 to which is secured a sleeve I4, which ts into a counterbore I5 in the rear end of the handle 4, and affords a bearing for the member I I of the drive shaft. The parts are maintained in the positions shown in Fig. 2, i. e. with the driving tongue I0 in the slot 9, by a thumb-screw I6 threaded through the handle 4 and sleeve I4 and having its inner end fitted within an annular groove I1 formed in the member II. Upon release of the thumb-screw I5, the member II, tongue I0 and sleeve I4 may be withdrawn from handle 4, thereby completely disconnecting the instrument from the flexible drive shaft S.

As illustrated diagrammatically in Fig. 13, the

other end of the exible vdrive shaft S is connected with a remotely located electric driving motor M for rotation thereby. Inasmuch as the construction of the motor M, the support therefor, and the specific means for transmitting rotary motion therefromto the shaft S may be conventional, and form no part of this invention, detailed illustration and description thereof are -deemed unnecessary.

Reciprocably mounted in vertically alined guideways I8 and I9 in the head 2 is a saw bar 2D having, in its lower end portion, a vertically disposed slot 2I into which is fitted the shank 22a of a toothed and rearwardly beveled saw blade 22 which is held against outward movement, relative to the saw bar 20, by its engagement with the head of ascrew 23 threaded into the bar. Endwise movement of the saw blade, relative to the saw bar, is prevented by a locating stud 24 (Fig. 2) carried by of which stud is tted into a notch 25 in the rear edge of the saw blade. To assist in properly positioning the saw blade in the saw bar, there is secured to the saw bar, by a screw 2S, a nger 21 the lower end of which is adapted to engage and form a stop for the upper end of the saw blade.

The saw bar and the saw blade carried thereby are reciprocated by the rotary motion of a crankpin 28 secured in a crank disk 29 on the forward end of the rotary shaft 8. The crank-pin 28 `carries a square block 3@ slidingly fitted in a transverse slideway 3| formed in a rearwardly projecting portion 32 of the saw bar. It will be noted that the teeth of the saw blade 22 are set to a width greater than the thickness of the blade and are so formed that the blade will effect a cutting operation on its up stroke. The saw bar 20 is held in its guideways I8 and I9 by a faceplate 33 secured to the head 2 by screws 34.

To separate the dura from the skull and to prevent contact of the saw blade with the dura,

,during a skull sawing operation, the instrument is provided with a ring-like saw guard and dura deflector member 35 which is passed through a trephined opening in the skull and surrounds the lower end of the saw blade, when the bade is in its lowermost position. The member 35 is vcarried by a shank 35 mounted for limited turnthe saw bar, the head ing movement in the head 2, as hereinafter will be explained.

As hereinbefore indicated, this instrument is designed to be used in conjunction with and as a supplement to the trephining instrument disclosed in my pending United States patent application Serial No. 653,900, now Patent No. 2,504,074. The instrument disclosed in that application is adapted to remove disks of bone from a skull K, thereby leaving holes t, one of which is shown in Fig. 11. After a pair of spaced holes have been trephined into the skull, the instrument disclosed in this application is used to make a saw cut c, of more or less circular shape from one hole to the other thereby leaving within the saw cut a portion in the form of a flap or trap door which is thereafter broken along a line between the pair of trephined holes to give access to the underlying dura d and the brain therebeneath. As hereinbefore stated, and as illustrated at g in Fig. 11, this saw cut is inclined relative to the surface of the skull so that the outer diameter of the nap f is greater than its inner diameter, thus facilitating repositioning and re-knitting of the flap j in its aperture. If desired, the instrument may be used to form a curved saw cut from a single trephined hole back to the same hole thereby completely removing the skull section.

During a sawing operation, the guard and deflector member 35 slides against' the under surface of the skull and separates the dura d from the skull K as illustrated in Fig. 1l. Slidingly contacting the outer surface of the skull is a slotted foot 31, pivotally mounted, on a screw 38, to the lower end of a shank 39 secured by screws 40 to the forward arm 4Ia of a two-armed level' 4I. The lever 4I is journaled on a shoulder screw 42 threaded into the head 2. A coil spring 43, surrounding a hub 44 on the head and into which the screw 42 is threaded, has one offset leg 43a engaging the head 2 and another leg 43b engaging the lever 4I. This spring normally biases the lever 4|, and the parts carried thereby, to the position illustrated in full lines in Fig. l.

The rear arm 4Ib of the lever 4I is in the form of a hand lever and underlies the handle 4. Thus a user may, by grasping the handle 4 and arm 4 Ib between the palm of the hand and the ngers, swing the lever 4I to the position indicated in dotted lines in Fig. l, in opposition to the spring 43. This causes the foot 31 to be lowered into contact with the outer surface of the skull, as shown in Fig. 11. A stud 45 carried by the arm 4Ib has a rounded head adapted to engage the underside of the head of a stopI screw 46 threaded into the frame I. Contact of the stud 45 with the screw 46 limits the upward movement of the lever-arm 4Ib and consequently the downward movement of the foot 31. In operation, the screw 46 is so adjusted that the foot 31 will lightly contact the outer surface of the skull bone when the guard 35 is contacting the inner. surface thereof. With the members 35 and 31 lightly engaging, but not gripping, the skull bone, the instrument will be steadied and guided while making the saw cut c. Adjustment of the stop screw 46 in the frame I permits the instrument to be adjusted to skull bones of various thicknesses.

Swinging of the lever 4I about its fulcrum 42 also is utilized to effect starting and stopping of the electric motor M and consequently starting 'and stopping of the reciprocation of the saw lblade 22. This is effected through the medium of a power control xelement" preferably in?. the'- nature of a super-sensitive self-opening switch, designated generally as T, secured upon the frame l. This switch may be of commercial form .and may be constructed substantially as disclosed in United States patent to McGall, No. 1,960,020, May 22, 1934. Inasmuch as the specific construction of this switch forms no part ofthe present invention, detailed illustration and description thereof is deemed unnecessary. Suii'ice it to say that it is embodied in an electric circuit (see Fig. 13) comprising a line L1 which extendsrom any suitable source of electric power to a coupling block 41 thence directly to the motor M. A line L2 extends to the coupling block 41 and thence to the switch T carried by the instrument. The switch is normally open but is adapted to be closed by the inner endwise movement of a spring plunger 48 forming a part of the switch. When the switch is closed, the line L2 is connected back to the coupling block 41 and then to the motor M through a line L3 thereby completing the circuit from the lines L1 and L2 to the motor and causing the latter to rotate and turn the exible cable I2, shaft 8 and crank disk 29, thus effecting reciprocation of the saw -bar 20 and the saw blade 22 carried thereby.

As shown in Figs. 4.- and 5, the lines L2 and L3 are preferably within a single cable N which passes through a metal tube P, secured to the handle 4 by metal straps R, attached to the handle by screws r.

Secured to the side of the switch block, by a screw 49, is an outwardly biased spring arm 50 adapted, when deflected, to engage the outer end of the plunger 48 thereby to shift it inwardly t0 close the circuit.

It will be seen from Fig. 13 that there is embodied, in the lines L2 and L3, a separable connector 5| having unlike iingers 5Ia and 5P adapted to enter complemental sockets 41*l and 41h, respectively, in the coupling block 41, to make contact with the lines L2 and L3 therein. These ngers and their complemental sockets may be of any suitable or preferred form but are so shaped that the block 41 and the connector 5I may be united in only one position and so that the connector may not be inadvertently inserted into a conventional electric socket.

The spring arm 5|! is adapted to be deected inwardly, toward the body of the switch T, to shift the plunger and actuate the switch to close the circuit, by the clockwise movement (Fig. 1) of a two-armed lever 52 fulcrumed on a shoulder screw 53 threaded into a hub 54 on the frame I. The upper arm 52a of the lever 52 is designed to engage the spring arm 50, while the lower arm 52b thereof is formed with a cam surface 55 adapted to be engaged by a stud 56 carried by the arm 41h of the lever 4|. A coil spring 51, surrounding the hub 54 and having one leg engaging the head 2 and another leg engaging the lever 52, normally tends to turn the lever 52 counterclockwise (Fig. 1) to move the arm 52a out of pressure contact with the switch spring arm 50, thus permitting the free end of that arm to move away from the plunger 48, which thereupon is moved outwardly to break the motor circuit and bring the saw to rest. The switch T is closed, to start the motor and saw, by counterclockwise movement of the lever arm 41h from the position shown in full lines in Fig. 1 to the position illustrated in dotted lines. This movement of the lever arm causes the stud 56 to act on the cam surface 55 and thereby turn the lever 52 clockwis'eyiiroppositfon'to the spring l51', to close the motor circuit as above described.

An important feature 'of this invention resides in the construction` which enables the instrument readily to make a saw cut c which is inwardly andv downwardly inclined relative to the router surface of the skull as indicated at g in Fig. 11. The angle ofthe cut c' is effected by the angular arrangement of the under or skull-contacting surface of the foot 3'1 relative to path of reciprocation. of' the saw blade 22,:as shown most clearly in Fig. 11.

.'a'motl'ierv important feature of the invention is the specific construction of the skull-contacting foot 31, by reason of which the foot is adapted to have ample contact with the skull to prevent wobbling of the instrument regardless of the size orv curvature ofthe skull. Tc that end, the lower surface of the footA 31 is formed with transverse grooves 31a and 31h leaving landsl 31c which serve as spaced contacts slidably t0 support the foot 31 on the' curved or irregular outer surface of the skull.

Still another important feature of this invention is the construction and arrangement of the parts which permit the saw cut to be made in an arc having a relatively short radius. This is effected by providing a relatively narrow saw blade, having its trailing edge portion beveled as indicated at 22a (Fig. 12), and 'by pivotally mounting the shank 36 of the guard and delector member 35 so that it maybe turned on a vertical axis a substantially parallel to and in line with the leading edge of the shank. Thus the shank may turn and adapt itself to and track the saw cut without binding therein. Because of its/narrow width, the set of its teeth, and its beveled trailing edge, the saw blade may, during the sawing operation, be maintained in a position in which it isat a substantial angle to thev cut which it is making, thus causing the saw to cut in a relatively small arc.

The upper end portion of the shank 36 is tted into a slot 58 formed in a holder member 59 and held therein by screws 6U. The member 59 is mounted for limited turning movement in an open-sided sleeve-like portion 2a* depending from theY under side of the head 2, as shown most clearly in: Figs. 2f and 7.. Adjacent its lower end, the holder member 59 is formed with a `ange 6i having therein a V-shaped notch 62 through which the saw blade passes. The opposed walls of the notchl 62 are so arranged that the holder member 59 and the sha-nk 36 may have their maximum turning movements in both directions withoutA bringing the walls of the notch 62 into contact with the saw blade. Surrounding the sleeve-like portion 2a is a semi-cylindrical shield member 63, `shown detached in Fig. 9, having a bottom` plate 63a provided with a slot 64, the outer portion of which has spaced parallel walls 64a, between which the saw blade 22- is reciprocated and which prevent material deflection of the saw blade, and an inner portion having walls 64b which are disposed at an angle to eachother and between which the shank 36 of the guard and deflector member 35 is located. Contact of the wallsltb by the shank 36, as indicated in full and dotted lines in Fig. I2, limits the turning movement of the holder member 59 and the shank 36 carried thereby. The shield 63 is formed with a perforated upstanding tab 65 through which passes one end of aA thumb screw 66 threaded into the head 2. This tab and thumb screw secure the shield member 63 upon the portion 2a of the head 2 and prevent its rotation thereon.

From the foregoing it will be apparent that this invention has provided an improved surgical saw particularly adapted for making an inclined arcuate saw cut, of large or small radius, in a skull bone to facilitate an operation on the brain therebeneath; which will protect the dura against damage; and which may be readily manipulated and controlled by the user.

Having thus set forth the nature of the invention, what I claim herein is:

1. A surgical instrument, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade carried thereby; a movable skull-contacting member carried by and movable relative to said frame; an electric switch carried by said frame and in circuit with said motor; and a common actuating member carried by the instrument for shifting said skull-contacting member and for actuating said switch to control said motor.

2. A completely organized unitary construction including a surgical instrument, comprising a frame; a handle secured to said frame; a rotary shaft journaled lengthwise of said handle; a saw bar reciprocably mounted in said frame and operated by the rotation of said shaft; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a flexible driving connection between said motor and said shaft for rotating the latter; an electric switch carried by said frame and a switch actuating member pivotally mounted on said handle on an axis arranged transversely of the handle, said member extending substantially the full length of the handle.

3. A surgical instrument, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade'carried thereby; a member movable relative to said frame and adapted to be moved into contact with the outer surface of a skull; an electric switch carried by said frame and in circuit with said motor; a lever carried by the instrument for supporting and moving said member; and means actuated by said lever to close said switch to start said motor.

4. A surgical instrument, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade carried thereby; a foot member movable relative to said frame and adapted to be moved into contact with the outer surface of a skull; an electric switch carried by said frame and in circuit with said motor; a manually operable lever carried by the instrument for supporting and moving said foot member; means actuated by said lever to close said switch to start said motor; and an adjustable stop to limit the movement of said lever and ,the foot member carried thereby.

5. A surgical instrument, comprising a frame; a handle secured to said frame; a saw bar reciprocably mounted in said frame; a saw blade se- 8, cured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade carried thereby; a two-armed lever pivotally mounted on said frame, one of said arms anording means for turning said lever about its pivot; a member carried by the other arm of said lever and movable thereby into contact with a skull; an electric switch carried by said frame and in circuit with said motor; and means actuated by the movement of said lever for closing said switch to Astart said` motor.

6; A surgical instrument comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade carried thereby; a manually actuable lever pivotally mounted on said frame; a member carried by one end of said lever and adapted to be brought into contact with a skull by movement of said lever; an electric switch carried by said frame and in circuit with said motor; and a switch actuating lever pivotally mounted on said frame and adapted to be turned about its pivot by the movement of the rst named lever to close said switch to start the motor.

7. A surgical instrument, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade carried thereby; a self-opening electric switch carried by said frame and in circuit with said motor; a spring biased switch-closing lever pivotally mounted intermediate its ends, on said frame and having one arm normally biased away from said switch; an-d a manually actuable lever pivotally mounted on said frame and adapted to engage the other arm of the iirst named lever to turn the same and cause it to close said switch to start the motor.

3. A surgical instrument, comprising a frame; a handle secured thereto; a saw bar reciprocably mounted in said frame; a saw blade secured to sai-d saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciproeating the latter and the saw blade carried thereby; a self-opening electric switch carried by said frame and in circuit with said motor; a switch closing lever pivotally mounted on said frame and normally biased away from said switch; a cam surface provided by said lever; a hand lever pivotally mounted on said frame and having a portion extending lengthwise of and adjacent to said handle; and means, carried by said hand lever and adapted to act on said cam surface, to shift said switch-closing lever to start the motor.

9. A surgical instrument, comprising a frame; a handle secured thereto and extending rearwardly therefrom; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; a rotatable driving member journaled in said frameY and extending lengthwise of said handle; means actuated by said driving member and connected with said saw bar for reciprocating the latter and the saw blade carried thereby; a power control element carried by said frame for rendering said driving member effective or ineirective to reciprocate said saw bar; an outer skull-contacting member; means normally mainammo? 9. taining. said skull-contacting member in a retracted position; and a manually operable lever pivoted on said frame `for supporting said skullcontacting member and for advancing it into skull-contacting position and 'for actuating said power control element.

10. A surgical instrument, comprising a frame; a handle secured thereto and extending rearwardly therefrom; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; a rotatable driving member journaled in said frame and extending lengthwise of said handle; means actuated by said driving member and connected with said saw bar for reciprocating the latter and the saw blade carried thereby; a power control element carried by said frame for rendering said driving member effective or ineffective to reciprocate said saw bar; inner and outer skull-contacting members, said inner member being secured to a sli-ank mounted for limited turning movement in said frame and said outer member being mounted for movement toward and from the outer surface of a skull; and a manually operable lever pivoted on said frame for supporting said outer member and for actuatingsaid power control element.

11.v A surgical instrument, comprising a frame; a handle secured thereto and extending. rearwardly therefrom; a sawv bar reciprocably mounted in said. frame; asaw blade secured to said saw bar; a rotatable driving member journaled in said frame and extending lengthwise of said handle; means actuated by said driving member and connected with said saw bar for reciprocating the latter and the saw blade carried thereby; a power control element carried by said frame for rendering said driving member effective or inelTective to reciprocate said saw bar; an inner skull-contacting member; means, including a relatively thin shank adapted to pass edgewise through a cut made by said saw blade', for supporting said skull-contacting member, said shank being mounted in said frame for limited turning movement about an axis substantially coincident with the forward edge of the shank; and a manually operable means on said frame for actuating said power control element.

12. A skull saw, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; means for reciprocating the saw bar and the saw blade carried thereby; a member adapted to be passed through an opening in a skull and to serve as a dura deflector and a guard for the lower end of said saw blade; and means, including a relatively thin shank adapted to pass edgewise through a cut made by said saw blade, for supporting said member, said shank being mounted in said frame for limited turning movement about an axis substantially parallel to and coincident with the forward edge of said shank.

13. A surgical instrument, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; power means to reciprocate said saw bar and the saw blade carried thereby; a combined dura deiiector and guard for the free end of said saw blade, comprising a member adapted to be inserted through an opening in a bone preparatory to a sawing operation; a foot member carried by and movable relative to said frame `and adapted to contact the outer surface of the bone during a sawing operation; a power control element carried by said frame and adapted to render said power means effective or ineffective to reciprocate said saw bar; and a member mounted on said frame and adapted simultaneously to shift said foot member. into contact with the bone and to actuate said power control element to eiect actuation of said saw bar.

14. A surgical instrument, as set forth in claim 13, in which the under face of the foot member is provided with a plurality of spaced bone-contacting surfaces adapted slidingly to support the foot member on the curved outer surface of the bone being sawed vand to prevent wobbling of the instrument during a sawing operation.

15. A surgical instrument, as set forth in claim 13, in which the foot member is pivotally supported and is provided on its under side 'with transversely arranged grooves and a plurality of spacedv lands adapted to contact the outer surface of the bone beingsawed, slidingly to support the instrument and prevent wobbling thereof 'during a sawing operation.

16. In a surgical saw having a frame, a relatively narrow reciprocating saw blade supported from said frame and having teeth along its front edge set to a width greater than the thickness of the blade, said blade having its rear edge portion beveled to reduce the thickness thereof to approximately one-half the maximum thickness of the blade, thus permitting the said blade to have a greater sidewise turning movement in a cut made by said teeth than would be possible if the blade were of uniform thickness throughout its width.

17. In a surgical saw, a relatively narrow reciprocating saw blade having teeth along its front edge set to a width greater than the thickness of the blade, said blade having its rear edge portion beveled thus permitting said blade to have a limited turning movement in a cut made by said teeth, and a guard for said saw blade comprising a portion surrounding the free end of the saw blade, said guard having a supporting shank adapted to pass edgewise through the cut made by said saw blade and pivoted to turn about an axis adjacent and substantially parallel to the forward edge of said shank.

18. In a surgical saw, a frame; a reciprocating saw bar mounted in said frame; a saw blade carried by and projecting from said saw bar; a guard for the free end of said saw blade, including a hub and a lat shank journaled for turning movement in said frame on an axis adjacent and substantially parallel to the forward edge of said shank, said shank being adapted to track a saw cut made by said saw blade; and a shield member for said saw blade and shank secured to said frame and provided with a bottom plate 'formed with a slot for the passage of said saw blade and shank, a portion of said slot having spaced angularly disposed walls between which said shank is free to turn.

19. A skull saw, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; power means to reciprocate said saw bar and the saw blade carried thereby; a foot member carried by and movable relative to said frame and adapted to contact the outer surface of a skull during a sawing operation, the skull-contacting surface of said foot being inclined to the path of reciprocation of said saw blade; a power control element carried by said frame and adapted to render said power means effective or ineiective to reciprocate said saw bar; and a member mounted on said frame and adapted simultaneously to shift said foot member into contact with the skull and to actuate said power control element to effect actuation of said saw bar.

20. A surgical instrument, comprising a frame; a saw bar reciprocably mounted in said frame; a saw blade secured to said saw bar; an electric motor located remotely from said instrument; a driving connection between said motor and said saw bar for reciprocating the latter and the saw blade carried thereby; a movable skull-contacting member carried by and movable relative to said frame; an electric switch carried by said frame and in circuit with said motor; and means carried by the instrument for simultaneously shifting said skull-contacting member and actuating said switch to control said motor.

21. In a surgical saw, a reciprocating saw bar provided with a longitudinal slot; a saw blad removably mounted in said slot; interengaging means between said saw bar and said saw blade to prevent endwise movement of said saw blade relative to said saw bar; and means to prevent edgewise movement of said saw blade out of said slot.

22. In a surgical saw, a reciprocating saw bar provided with a longitudinal slot; a saw blade fitted edgewise into said slot and having a notch therein; means in said slot and engaging the walls of said notch for preventing endwise movement of said saw blade relative to said saw bar; and means to prevent edgewise movement of said saw blade out of said slot.

12 23. In a surgical saw, a reciprocating saw bar provided with a longitudinal slot; a saw blade. having a notch therein, tted edgewise into said slot; a stud fitted into said saw bar in alignment with said slot, said stud being adapted to engage the Walls of said notch to prevent endwise movement of said saw blade relative to said saw bar; a stop member carried by said saw bar and adapted to engage the upper end of said saw blade to align the notch therein with said stud; and removable means carried by said saw bar and engaging said saw blade to prevent edgewise movement of said saw blade out of said slot.

JOHN D. KARLE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

